[librsvg] font_props: improve comments

[Federico Mena Quintero <federico src gnome org>]

commit 07d114f5cabd03af11b5addc238d710a0f0f737c
Author: Paolo Borelli <pborelli gnome org>
Date:   Sat Aug 11 10:04:37 2018 +0200

    font_props: improve comments
    
    Drop outdated comment about macro, also we explicitely decided
    against Weight(w) since the spec has a fixed set of weights.
    Add a reference link also for font size.

 rsvg_internals/src/font_props.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/rsvg_internals/src/font_props.rs b/rsvg_internals/src/font_props.rs
index db2408a0..5a5670dc 100644
--- a/rsvg_internals/src/font_props.rs
+++ b/rsvg_internals/src/font_props.rs
@@ -6,6 +6,7 @@ use length::{Length, LengthDir, LengthUnit, POINTS_PER_INCH};
 use parsers::{Parse, ParseError};
 use state::ComputedValues;
 
+// https://www.w3.org/TR/2008/REC-CSS2-20080411/fonts.html#propdef-font-size
 #[derive(Debug, Copy, Clone, PartialEq)]
 pub enum FontSizeSpec {
     Smaller,
@@ -118,8 +119,8 @@ pub enum FontWeightSpec {
     Bold,
     Bolder,
     Lighter,
-    W100, // FIXME: we should use Weight(100),
-    W200, // but we need a smarter macro for that
+    W100,
+    W200,
     W300,
     W400,
     W500,